Methods And Systems For Performing Medical Procedures With Reference To Projective Image And With Respect To Pre-Stored Images

ABSTRACT

A catheter is navigated within a body cavity of a patient. This navigation is enabled by the provision of the transmitter of electromagnetic radiation under platform, a receiver of electromagnetic radiation rigidly attached to fluoroscope, and a receiver of radiation rigidly attached to the catheter, all three of which are connected by wires to a computer. The computer displays, on a display unit, the image of the body cavity acquired by the fluoroscope, with an icon representing the catheter superposed on the image in the location and orientation of catheter relative to the body. There is no representational imaging device equipped with a receiver in the apparatus of the current invention.

RELATED APPLICATIONS

This application is a divisional of and claims priority to U.S. patentapplication Ser. No. 10/169,186 filed Jun. 28, 2002 entitled Methods AndSystems For Performing Medical Procedures With Reference To ProjectiveImage And With Respect To Pre-Stored Images, which claims priority toInternational Patent Application No. PCT/US01/00074, InternationalFiling Date Jan. 2, 2001, entitled Methods And Systems For PerformingMedical Procedures With Reference To Projective Images And With RespectTo Pre-Stored Images, which claims benefit of U.S. ProvisionalApplication Ser. No. 60/175,226 filed Jan. 10, 2000 entitledInterventional 3D Fluoroscope, all of which are hereby incorporatedherein by reference.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to medical procedures that are performedwith reference to images of the patient and, more particularly, tomedical procedures performed with reference to projective images such asfluoroscope images, and also to medical procedures performed withreference to images acquired prior to, and independently of, theprocedures.

Images of the interiors of patients commonly arc used to guide theperformance of invasive medical procedures on the patients. Bucholtz, inU.S. Pat. No. 5,383,454, Ferre et al., in U.S. Pat. No. 5,829,444 andU.S. Pat. No. 5,873,822, and Bourman, in U.S. Pat. No. 5,902,239, teachthe navigation of a probe, such as a catheter, within the body of apatient, with reference to previously acquired images. Barrick, in U.S.Pat. No. 5,772,594, teaches fluoroscopic imaging of a bone prior to theinsertion therein of a guide pin or screw with reference to the image.

Two kinds of imaging modalities are in common use. Representationalimages, such as CT images, MR images and ultrasound images, representphysical properties of the patient's body at particular locationstherein. For example, each pixel of a 2D digital ultrasound image of apatient represents an acoustic impedance contrast at a correspondingpoint inside the patient's body, and each voxel of a 3D CT image volumerepresents the density of the patient's body tissue at a correspondingpoint inside the patient's body. Projective images, such as fluoroscopicX-ray images, represent projections of physical properties of thepatient's body into a plane. For example, each point in a fluoroscopicX-ray image is an integral along a ray, from the X-ray source to theX-ray image, of the density of the patient's body tissue.

Two prior art references of particular note are Gilboa et al., WO00/10456 and WO 00/16684, both of which documents are incorporated byreference for all purposes as if fully set forth herein. WO 00/10456teaches intra-body navigation of a probe in conjunction with imaging bya C-mount fluoroscope. WO 00/16684 teaches the use of a representationalimaging device, such as an ultrasound probe, in conjunction with theC-mount fluoroscope of WO 00/10456, for the purpose of identifying andrecording points-of-interest, within the body of the patient, towardswhich the probe subsequently is navigated. FIG. 1A, which is adaptedfrom FIG. 2 of WO 00/16684, shows a patient 24 lying on an operationplatform 34 and being imaged by a C-mount fluoroscope 22. A catheter 26is navigated within a body cavity 28 of patient 24. This navigation isenabled by the provision of a transmitter 30 of electromagneticradiation under-platform 34, a receiver 40 of electromagnetic radiationrigidly attached to fluoroscope 22, and a receiver 32 of radiationrigidly attached to catheter 26, all three of which are connected bywires 51 to a computer 50. Fluoroscope 22 is used to acquire an image ofa portion of the body of patient 24 that includes body cavity 28. Asexplained in WO 00/10456, transmitter 30 defines a reference frame, andthe signals received by computer 50 from receivers 40 and 32 in responseto the electromagnetic radiation transmitted by transmitter 30 areindicative of the locations and orientations of fluoroscope 22 andcatheter 26 relative to the reference frame. Given these locations andorientations, computer 50 displays, on a display unit 48, the image ofbody cavity 28 acquired by fluoroscope 22, with an icon representingcatheter 26 superposed on the image in the true location and orientationof catheter 26 relative to body cavity 28.

Because patient 24 may move, relative to platform 34, during the medicalprocedure, patient 24 also is provided with a receiver 38 ofelectromagnetic radiation. Computer 50 computes, from the signalsreceived from receiver 38 in response to the electromagnetic radiationtransmitted by transmitter 30, the location and orientation of the bodyof patient 24 relative to the reference frame. This is in addition tothe computation, by computer 50, from the signals received from receiver40, of the location and orientation of fluoroscope 22 relative to thereference frame, and in addition to the computation, by computer 50,from the signals received from receiver 32, of the location andorientation of catheter 26 relative to the reference frame. Computer 50records the location and orientation of patient 24 when the image ofbody cavity 28 is acquired. If patient 24 does moves, computer 50adjusts the joint display of the image and the catheter icon on displayunit 48 to reflect the movement of patient 24. so that the catheter iconalways is displayed in a manner that reflects the true location andorientation of catheter 26 relative to body cavity 28.

As alternatives to receivers 32 and 44, catheter 26 and patient 24 areprovided with respective imageable markers 46 and 44. Computer 50locates the shadows of markers 46 and 44 in the image, using standardimage processing techniques, and computes, from the locations of theseshadows, the locations and orientations of catheter 26 and patient 24.

A representational imaging device 52, equipped with a receiver 40 a ofelectromagnetic radiation, also is provided, to acquire arepresentational image of a portion of the body of patient 24 thatoverlaps with the portion of the body of patient 24 that is acquiredusing fluoroscope 22. Computer 50 computes, from the signals receivedfrom receiver 40 a in response to the electromagnetic radiationtransmitted by transmitter 30, the location and orientation of imagingdevice 52 relative to the reference frame. Computer 50 then displays therepresentational image, on display unit 48, superposed on the imageacquired by fluoroscope 22, so that a point-of-interest, towards whichcatheter 26 is to be navigated, can be picked on display unit 48, evenprior to the introduction of catheter 26 into body cavity 28. Improvedmethods of effecting this superposition are taught by Gilboa et al. inPCT application US99/26826, which also is incorporated by reference forall purposes as if fully set forth herein. Because computer 50 tracksthe movement of both patient 24 and catheter 26, an icon representingthe point-of-interest is displayed on display unit 48 in a manner thatrepresents the true location of the point-of-interest in body cavity 28,so that catheter 26 can be navigated Jo the point-of-interest withreference to the relative locations, as displayed by display unit 48, ofthe icon representing catheter 26 and of the icon representing thepoint-of-interest.

Representational imaging device 52 may be external to the body ofpatient 24, as illustrated in FIG. 1A, or internal to the body ofpatient 24. The specific example of representational imaging device 52that is presented in WO 00/16684 is an intracardiac ultrasound probethat is used to image and identify the fossa ovalis of the cardiacseptum and one or more of the openings of pulmonary veins. These pointswithin the heart may be targets of ablation for treating atrialfibrillation, and so constitute points-of-interest within the heart (asbody cavity 28) of patient 24. Following the representational imaging ofthese targets by intracardiac ultrasound probe 52 and the picking of thepoints-of-interest, intracardiac ultrasound probe 52 is withdrawn and anablating catheter 26 is navigated towards the points-of-interest.

Transmitter 30 is an example of what is called in WO 00/16684 a“locating implement”. Receivers 32, 38, 40 and 40 a are examples of whatis called in WO 00/16684 “location implements”. Transmitter 30, togetherwith receiver 32, 38, 40 or 40 a constitute what is called in WO00/16684 a “locating system”. In the present context, the location andthe orientation of an object are called the “disposition” of the object,so what WO 00/16684 calls a “locating system” is called herein a“disposing system”. Similarly, what WO 00/16684 calls a “locatingimplement” is called herein a “disposing implement”, and what WO00/16684 calls a “location implement” is called herein a “dispositionimplement”. The term “location system” is used herein to refer, not onlyto systems that measure both the location and the orientation of anobject, but also to systems that measure only the location of an object;such a system includes a locating implement and a location implement.Note that when multiple disposing systems are used, one disposinginstrument may be shared by all the disposing systems as is the casewith transmitter 30, in which case the shared disposing instrumentdefines a common reference frame for all the disposing systems; or,alternatively, one disposition implement may be shared by all thedisposing systems, in which case the shared disposition instrumentdefines a common reference frame for all the disposing systems. Commonexamples of disposing systems include electromagnetic disposing systems,magnetic disposing systems, acoustic disposing systems and stereopairoptical systems.

One invasive medical procedure for which the prior art methods are notquite suitable is the deployment of a stent in a partially blockedcoronary artery. This procedure commonly is performed by injecting acontrast agent into the target coronary artery tree and then navigatinga catheter that bears the stent towards the target blockage with thehelp of X-ray angiographic images acquired in real time by a fluoroscopesuch as fluoroscope 22. In this case, the points-of-interest are theblockage itself, and the branches of the coronary artery tree that mustbe traversed on the way to the blockage. In principle, the prior artdiscussed above can be used to identify the points-of-interest, providedthat these points-of-interest can be picked on the image provided byrepresentational imaging device 52. For example, representationalimaging device 52 may be a CT scanner: the contrast agent, being X-rayopaque, shows up in both the projective images acquired usingfluoroscope 22 and the representational CT scan acquired using the CTscanner. This has the disadvantage of requiring the use of two imagingmodalities, one of which (CT) is not suitable for real-time imaging.Furthermore, it is relatively difficult to register a CT image volumewith a fluoroscopic image.

There is thus a widely recognized need for, and it would be highlyadvantageous to have, a method, of navigating a probe to apoint-of-interest in a body cavity of a patient, that is based on asingle projective imaging modality.

A CT scanner produces its representational image volume by appropriateprocessing (typically, by backprojection) of a set of projective images.In principle, then, it should be possible to use fluoroscope 22 itselfas both a projective imager and a representational imager. Yeung, inU.S. Pat. No. 5,588,033, which is incorporated by reference for allpurposes as if fully set forth herein, teaches the reconstruction of abinary (two-level) image volume from a relatively small set ofprojective radiographic images. In principle, a similar reconstructionshould be possible using fluoroscopic images acquired at differentdispositions relative to patient 24. In particular, in the stentdeployment discussed above, a binary representational image volume ofthe contrast agent in the coronary artery tree would show the portion ofthe coronary artery tree that contains the contrast agent at one of thetwo display levels (e.g., “1”) and the rest of the imaged portion of thepatient's body at the other level (e.g., “0”), and so would suffice toallow picking of the points-of-interest. In practice, however,fluoroscope 22 lacks sufficient mechanical stability to allow accuratereconstruction of even a binary image volume. Known successfulreconstructions of image volumes from 2D projective images all requirevery accurate positioning of the imaging apparatus. Conventional CTscanners include heavy and very accurate mechanisms for rotating theirX-ray sources and detectors and similarly heavy and accurate slidingmechanisms for moving the platform on which the patient lies. Yeung usesa stereotactic localizer frame to provide the required dispositionalaccuracy.

There is thus a widely recognized need for, and it would be highlyadvantageous to have, a method of transforming a set of projectiveimages, acquired using a projective imager of limited mechanicalstability, into a representational image volume.

Returning to the procedure for deploying a stent in a coronary artery,the fluoroscope commonly is placed in a disposition relative to thepatient that is expected to give the best projective view of the targetcoronary artery tree. The contrast agent is injected into the coronarytree, and the projective image is acquired and digitized. Thisprojective image is used as a background “road map” for catheternavigation with the help of other images subsequently acquired of thetarget coronary artery tree, but only if the fluoroscope and the patientremain in the same relative disposition. Movement of either thefluoroscope or the patient renders this projective image useless as aroad map. In particular, if the disposition of the fluoroscope relativeto the patient turns out to be suboptimal, or if the patient must beimaged from several dispositions of the fluoroscope in order to give anadequate picture of the three-dimensional structure of the coronaryartery tree, then for each new disposition of the fluoroscope, thecontrast agent must be injected anew and a new road map must beacquired. This exposes both the medical team and the patient toadditional X-radiation, and also exposes the patient to the danger ofliver damage from repeated injections of the contrast agent.

There is thus a widely recognized need for, and it would be highlyadvantageous to have, a method of acquiring and using X-ray angiographicroad maps without undue danger to either the patient or the medicalteam.

SUMMARY OF THE INVENTION

According to the present invention there is provided a method ofnavigating a probe to a target point-of-interest in a body cavity of apatient, including the steps of: (a) acquiring a plurality of projectiveimages of at least a portion of the body cavity, using a projectiveimaging device, each projective image being acquired with the projectiveimaging device in a different respective disposition relative to areference frame; (b) for each projective image, measuring the respectivedisposition of the projective imaging device; (c) estimating a locationof the target point-of-interest, relative to the reference frame, fromthe protective images, the estimating being based on the measureddispositions of the projective imaging device; (d) inserting the probeinto the body cavity; (e) measuring a location of the probe relative tothe reference frame; and (f) moving the probe, within the body cavity,so as to minimize a difference between the measured location of theprobe and the estimated location of the target point-of-interest.

According to the present invention there is provided a navigating systemfor navigating a probe to a point-of-interest in a body, cavity of apatient, including: (a) a projective imaging device for acquiring aplurality of projective images of at least a portion of the body cavity;(b) a disposing system for measuring, for each projective image, arespective disposition of the projective imaging device relative to areference frame; (c) a mechanism for estimating a location of thepoint-of-interest, relative to the reference frame, from the projectiveimages, the estimating being based on the measured dispositions of theprojective imaging device; and (d) a locating system for measuring alocation of the probe relative to the reference frame.

According to the present invention there is provided a method ofacquiring an image volume of a body, including the steps of: (a) foreach of a plurality of nominal dispositions of a projective imagingdevice relative to a reference frame: (i) measuring an actualdisposition of the projective imaging device relative to the referenceframe, (ii) if the actual disposition is not substantially the same asthe each nominal disposition, moving the projective device until theactual disposition is substantially the same as the each nominaldisposition, and (iii) acquiring a respective projective image of thebody, using the projective imaging device at the each nominaldisposition; and (b) transforming the plurality of projective imagesinto the image volume.

According to the present invention there is provided an imaging systemfor acquiring an image volume of a body, including: (a) a projectiveimaging device for acquiring projective images of the body; (b) adisposing system for measuring dispositions of the projective imagingdevice relative to a reference frame; (c) a mechanism for moving theprojective imaging device among a plurality of nominal dispositionsthereof, with reference to the measured disposition; and (d) a processorfor transforming the projective images into the image volume, eachprojective image having been acquired at a different respective nominaldisposition.

According to the present invention there is provided a method ofacquiring an image volume of a body, including the steps of: (a) foreach of a plurality of dispositions of a projective imaging devicerelative to a reference frame: (i) moving the imaging device to thedisposition, as measured by a disposing system, and (ii) acquiring arespective projective image of the body; and (b) transforming theprojective images into the image volume according to the measurements ofthe dispositions.

According to the present invention there is provided an imaging systemfor acquiring an image volume of a body, including: (a) a projectiveimaging device for acquiring projective images of the body; (b) adisposing system for measuring dispositions of the projective imagingdevice relative to a reference frame; and (c) a processor fortransforming the projective images into the image volume according tothe measured dispositions.

According to the present invention there is provided a method ofacquiring an output image volume of a body, including the steps of: (a)for each of a plurality of actual dispositions of a projective imagingdevice: (i) moving the projecting imaging device to the each actualdisposition, and (ii) acquiring a respective projective image of thebody, using the projective imaging device at the each actualdisposition; (b) based on the projective images, estimating the actualdispositions; and (c) based on the estimated dispositions, transformingthe projective images into the output image volume.

According to the present invention there is provided an imaging systemfor acquiring an image volume of a body, including: (a) a projectiveimaging device for acquiring a plurality of projective images of atleast a portion of the body at actual respective dispositions of theprojective imaging device; and (b) a processor for estimating the actualdispositions from the projective images and for transforming theprojective images into the image volume, the transforming being based onthe estimated dispositions.

According to the present invention there is provided a method ofnavigating a probe in a body cavity of a patient, including the stepsof: (a) acquiring a plurality of images of at least a portion of thebody cavity, using an imaging device, while measuring, for each image, arespective disposition of the imaging device relative to a referenceframe, each image being acquired at a different respective disposition;(b) selecting one of the first images to use as a guide image; and (c)displaying the guide image along with an icon representative of adisposition of the probe within the body cavity.

According to the present invention there is provided a method oftreating a body of a patient, including the steps of: (a)simultaneously: (i) acquiring a first image of at least a portion of thebody, using an imaging device, (ii) measuring a disposition of theimaging device relative to a reference frame, and (iii) measuring adisposition of the body relative to the reference frame; (b) restoringthe imaging device and the body to respective dispositions that areequivalent to the measured dispositions; and (c) performing a medicalprocedure on the body with reference to the first image after therestoring of the imaging device and of the body to the equivalentdispositions.

According to the present invention there is provided a method oftreating a body of a patient, including the steps of: (a)simultaneously: (i) acquiring a first image of at least a portion of thebody, using an imaging device, (ii) measuring a disposition of theimaging device relative to a reference frame, and (iii) measuring afirst disposition of the body relative to the reference frame; (b)measuring a second disposition of the body relative to the referenceframe; and (c) performing a medical procedure on the body with referenceto the first image and with reference to all three dispositions.

The patient upon whom the methods of the present invention are practicedcould be either a person or an animal. The term “medical procedure” asused herein should be construed as including veterinary procedures.

The term “probe” as used herein should be construed as including anydevice or instrument, such as a catheter, an endoscope or a surgicaltool, that is introduced to the body of a patient and that is navigatedtowards a target for the purpose of performing a medical procedure. Themedical procedures that fall within the scope of the present inventioninclude but are not limited to diagnostic procedures and therapeuticprocedures, including surgical procedures.

According to a first aspect of the present invention, a plurality ofprojective images of at least a portion of a body cavity are acquired bya projective imaging device such as fluoroscope 22 at differentrespective dispositions relative to a reference frame, while measuringthese dispositions, for example by using a disposing system. Eachprojective image includes a point that corresponds to a targetpoint-of-interest in the body cavity; these points in the projectiveimages are termed herein “projections” of the target point-of-interest.A location of the point-of-interest, relative to the reference frame, isestimated, preferably by picking the projections of thepoint-of-interest on two or more projective images, constructing rayscorresponding to the picked projections, and computing the location,relative to the reference frame, of the point-of-nearest-mutual-approachof the rays. The projections may be picked manually. Alternatively, theprojections are picked manually on a first projective image andautomatically on subsequent projective images, for example by usingstandard image processing and feature recognition techniques to trackthe projection from image to image. Alternatively, the projective imagesare displayed successively and repeatedly, along with an icon thatrepresents a point in space. The coordinates of the point are varieduntil the icon substantially coincides with all the projections.Alternatively, the projective images are transformed into an imagevolume, preferably by backprojection, and the target point-of-merest ispicked directly in the image volume.

With the location of the target point-of-interest relative to thereference frame now known, a probe is inserted in the body cavity. Thelocation of the probe is measured, preferably using a locating system,and the probe is moved towards the target point-of-interest.

Preferably, a contrast agent is introduced to the imaged portion of thebody cavity prior to imaging.

Preferably, the location of at least one intermediate point-of-interest,relative to the reference frame, also is estimated from the projectiveimages, and the probe is moved towards the target point of interest withreference to a display of icons that represent the estimated locationsof the points-of-interest and the measured location of the probe. Thisdisplay may be from any convenient point of view. In particular, thisdisplay may be from a point of view different from the points of viewfrom which the projective images were acquired.

A system for implementing the first aspect of the present inventionincludes a projective imaging device for acquiring the projectiveimages; a disposing system for measuring the disposition of theprojective imaging device relative to the reference frame as the imagesare acquired; a mechanism for estimating the location of thepoint-of-interest relative to the reference frame, based on the acquiredimages; and a locating system for measuring the location of the probe inthe reference frame.

Preferably, the disposing system includes a disposition implementassociated with the projective imaging device and a disposing implementassociated with the reference frame. Alternatively, the disposing systemincludes a disposing implement associated with the projective imagingdevice and a disposition implement associated with the reference frame.Preferably, the disposing system is an electromagnetic disposing system,a magnetic disposing system, an acoustic disposing system or astereopair optical system.

Preferably, the locating system includes a location implement associatedwith the projective imaging device and a locating implement associatedwith the reference frame. Alternatively, the locating system includes alocating implement associated with the probe and a location implementassociated with the reference frame. Preferably, the locating system isan electromagnetic locating system, a magnetic locating system or anacoustic locating system.

The accurate transformation of projective images into an image volume isaddressed by a second aspect of the present invention, intended for usewith a relatively mechanically unstable projective imaging device suchas fluoroscope 22.

According to a first variant of the second aspect of the presentinvention, the projective images are transformed into the image volume,preferably by backprojection, according to respective nominaldispositions of the projective imaging device relative to a referenceframe. To ensure that the projective imaging device really is in thesenominal dispositions when the projective images are acquired, the actualdispositions of the projective imaging device are measured. If an actualdisposition differs from the corresponding nominal disposition, theprojective imaging device is moved until the actual dispositionsubstantially coincides with the nominal disposition, and only then isthe corresponding image acquired. The projective image device may bemoved manually, or automatically via a feedback loop. The correspondingimaging system includes the projective imaging device, a disposingsystem for measuring the dispositions of the projective imaging device,a mechanism for moving the projective imaging device to make the actualdispositions coincide with the nominal dispositions, and a processor fortransforming the projective images into the image volume.

According to a second variant of the second aspect of the presentinvention, the dispositions of the projective imaging device aremeasured explicitly as the projective images are acquired, and theacquired projective images are transformed into the image volumeaccording to the measured dispositions, preferably by backprojection.The corresponding imaging system includes the projective imaging device,a disposing system for measuring the dispositions of the projectiveimaging device, and a processor for transforming the projective imagesinto the image volume according to the measured dispositions of theprotective imaging device.

Preferably, the disposing system, of the devices of the first and secondvariants of the second aspect of the present invention, includes adisposition implement associated with the projective imaging device anda disposing implement associated with the reference frame.Alternatively, this disposing system includes a disposing implementassociated with the projective imaging device and a dispositionimplement associated with the reference frame. Preferably, thisdisposing system is an electromagnetic disposing system, a magneticdisposing system, an acoustic disposing system or a stereopair opticalsystem.

According to a third variant of the second aspect of the presentinvention, the projective images are transformed into the image volume,preferably by backprojection, according to respective actualdispositions of the projective imaging device. Because these actualdispositions are not known initially with sufficient accuracy to effectthe transformation, these actual dispositions are estimated from theprojective images themselves, and the transformation then is based onthe estimated dispositions. Preferably, the estimating of the actualdispositions is effected by transforming the projective images into aworking image volume, on the assumption that the images were acquired atrespective computational dispositions of the projective imaging device;and then correcting the computational dispositions, on the basis of thepreliminary image volume, to obtain the estimated dispositions.Preferably, the correcting of the computational dispositions is effectedby, for each computational disposition, computing a respective syntheticprojective image from the working image volume; comparing the syntheticprojective image to the corresponding acquired protective image;estimating, based on the comparison, the difference between thecomputational disposition and the actual disposition; and adjusting thecomputational disposition by subtracting this difference from thecomputational disposition. This transforming of the acquired projectiveimages into the working image volume, and this correcting of thecomputational dispositions, are iterated until the estimated differencesbetween the computational dispositions and the actual dispositions arenegligible.

The imaging system of the third variant of the second aspect of thepresent invention includes the projective imaging device and a processorfor performing the relevant calculations.

Preferably, in all three variants of the second aspect of the presentinvention, the projective imaging device is a fluoroscope.

According to a third aspect of the present invention, directed atnavigating a probe within the body cavity of the patient, a plurality offirst images of at least a portion of the body cavity is acquired atdifferent respective dispositions of the imaging device relative to areference frame, while measuring these dispositions. One of the firstimages is selected as a guide image, and the guide image is displayedalong with an icon that represents the true disposition of the probewithin the body cavity.

Preferably, the dispositions of the imaging device are measured using adisposing system that includes a disposition implement associated withthe imaging device and a disposing system associated with the referenceframe. Alternatively, the dispositions are measured using a disposingsystem that includes a disposing implement associated with the imagingdevice and a disposition implement associated with the reference frame.Preferably, the disposing system is an electromagnetic disposing system,a magnetic disposing system, an acoustic disposing system or astereopair optical system.

Preferably, a contrast agent is introduced to the portion of the bodythat is to be imaged prior to acquiring the plurality of first images.

To facilitate the correct display of the icon, the disposition of theprobe relative to the common reference frame also is measured.Preferably, the disposition of the probe is measured using a disposingsystem that includes a disposition implement associated with the probeand a disposing implement associated with the reference frame.Alternatively, the disposition of the probe is measured using adisposing system that includes a disposing implement associated with theprobe and a disposition implement associated with the reference frame.Preferably, the disposing system is an electromagnetic disposing system,a magnetic disposing system or an acoustic disposing system.

Also according to the third aspect of the present invention, directedtowards invasive medical procedures generally, a first image of at leasta portion of the body of a patient is acquired while measuring both thedisposition of the imaging device and the disposition of the patientrelative to a common reference frame. Subsequently, both the body of thepatient and the imaging device are restored to dispositions that areequivalent to the dispositions of the body of the patient and of theimaging device when the first image was acquired, and a medicalprocedure is performed on the body of the patent with reference to thefirst image. “Equivalent dispositions”, as understood herein, means thatthe disposition of the body of the patient relative to the imagingdevice (or. equivalently, of the imaging device relative to the body ofthe patient) after restoration is the same as when the first image wasacquired.

Preferably, the dispositions of the body of the patient and of theimaging device are measured using disposing systems that includerespective disposition implements associated with the imaging device andwith the body of the patient and a common disposing system associatedwith the reference frame. Alternatively, the dispositions are measuredusing disposing systems that include respective disposing implementsassociated with the imaging device and with the body of the patient anda common disposition implement associated with the reference frame.Preferably, the disposing systems are electromagnetic disposing systems,magnetic disposing systems, acoustic disposing systems or stereopairoptical systems.

Preferably, a contrast agent is introduced to the portion of the bodythat is to be imaged prior to acquiring the first image.

Preferably, the medical procedure includes navigating a probe to apoint-of-interest in the targeted portion of the patient's body, withreference to the first image.

Preferably, after the body of the patient and the imaging device arerestored to their equivalent dispositions, a second image is acquired,and the medical procedure is performed with reference to both images. Ifthe medical procedure includes navigating a probe to a point-of-interestin the targeted portion of the patient's body, then the disposition ofthe probe relative to the common reference frame also is measured.Preferably, the disposition of the probe is measured using a disposingsystem that includes a disposition implement associated with the probeand a disposing implement associated with the common reference frame.Alternatively, the disposition of the probe is measured using adisposing system that includes a disposing implement associated with theprobe and a disposition implement associated with the common referenceframe. Preferably, the disposing system is an electromagnetic disposingsystem, a magnetic disposing system or an acoustic disposing system.

Also according to the third aspect of the present invention, directedtowards invasive medical procedures generally, a first image of at leasta portion of the body of a patient is acquired while measuring both thedisposition of the imaging device and the disposition of the patientrelative to a common reference frame. Subsequently, the disposition ofthe patient is measured again, in case the patient has moved since thefirst disposition measurements, and a medical procedure is performed onthe patient with reference to both the first image and all threemeasured dispositions.

Preferably, the dispositions of the body of the patient and of theimaging device are measured using disposing systems that includerespective disposition implements associated with the imaging device andwith the body of the patient and a common disposing system associatedwith the reference frame. Alternatively, the dispositions are measuredusing disposing systems that include respective disposing implementsassociated with the imaging device and with the body of the patient anda common disposition implement associated with the reference frame.Preferably, the disposing systems are electromagnetic disposing systems,magnetic disposing systems, acoustic disposing systems or stereopairoptical systems.

Preferably, a contrast agent is introduced to the portion of the bodythat is to be imaged prior to acquiring the first image.

Preferably, the medical procedure includes navigating a probe to apoint-of-interest in the targeted portion of the patient's body. Thisnavigation includes measuring the disposition of the probe relative tothe common reference frame. Preferably, the disposition of the probe ismeasured using a disposing system that includes a disposition implementassociated with the probe and a disposing implement associated with thecommon reference frame. Alternatively, the disposition of the probe ismeasured using a disposing system that includes a disposing implementassociated with the probe and a disposition implement associated withthe common reference frame. Preferably, the disposing system is anelectromagnetic disposing system, a magnetic disposing system or anacoustic disposing system.

Under the third aspect of the present invention, the imaging device maybe either a protective imaging device or a representational imagingdevice, so that the first image may be either a projective image or arepresentational image. The preferred projective imaging device is afluoroscope.

An important difference between prior art computer-aided surgery and thefirst and third aspects of the present invention should be noted. Inprior art computer-aided surgery, if a 3D image volume is used to guidethe navigation of a surgical tool within the patient, then this imagevolume is acquired prior to surgery. That guide image volume then mustbe registered to the frame of reference of the disposing system that isused to track the surgical tool. Because the locations of theintermediate points of interest of the first aspect of the presentinvention, as well as the guide image of the third aspect of the presentinvention, are acquired with the help of location and dispositionsystems that share a common component that is associated with a commonreference frame, no such registration is necessary. For example, in FIG.1A, the location system (under the first aspect of the presentinvention) or the disposition system (under the third aspect of thepresent invention) for catheter 26 includes transmitter 30 and receiver32; the disposition system for fluoroscope 22 includes transmitter 30and receiver 40; and the disposition system for the body of patient 24includes transmitter 30 and receiver 38, with a common reference framefor all three receivers 32, 38 and 40 being defined by commontransmitter 30.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1A (prior art) illustrates a system for intra-body navigation of aprobe towards a point-of-interest in a body cavity of a patient, withthe help of a protective imaging device and a representational imagingdevice;

FIG. 1B shows the system of FIG. 1A modified according to the presentinvention by the removal of the representational imaging device,

FIG. 2 (prior art) is a more detailed illustration of the C-mountfluoroscope of FIGS. 1A and 1B;

FIG. 3 illustrates the near intersection of three rays;

FIG. 4 shows further details of the mechanical construction of thefluoroscope of FIG. 1 as modified for the purposes of the presentinvention;

FIG. 5 illustrates the backprojection algorithm of the presentinvention;

FIG. 6 is a flow chart for iteratively estimating actual dispositions atwhich the fluoroscope of FIG. 1 acquired a set of projective imageswhile refining an image volume constructed from those projective images.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is of a method of performing invasive medicalprocedures with the help of a single imaging device, particularly withthe help of a single projective imaging device such as a fluoroscope.Specifically, the present invention can be used to facilitate intrabodynavigation of a probe in a medical procedure such as stent deployment ina coronary artery.

The principles and operation of invasive medical procedures according tothe present invention may be better understood with reference to thedrawings and the accompanying description.

The present invention is explained herein with reference to stentdeployment in a coronary artery as an example of an invasive medicalprocedure. This example is merely illustrative, and should not beconstrued as limiting the scope of the present invention, which isapplicable to any invasive medical procedure that requires intra-bodynavigation of a probe to a point-of-interest.

Referring again to the drawings, FIG. 1B, which is identical to FIG. 1Awith representational imaging device 52 and receiver 40;* removed,illustrates a system of the present invention. In the context of theexample of deployment of a stent in a coronary artery, body cavity 28represents a coronary artery tree and catheter 26 is a catheter that isused to carry the stent to the blockage.

FIG. 2 illustrates C-mount fluoroscope 22 in .more detail, in schematiccross-section. C-mount fluoroscope 22 is based on a C-arm 60. At one endof C-arm 60 is an X-ray source 62 that includes an X-ray tube 63 and acollimator 64. At the other end of C-arm 60 is an imaging tube 66 thatincludes an anti-scatter grid 68, an image intensifier 70 and a CCDcamera 72. Collimator 64 blocks the X-rays emerging from X-ray tube 63except at an aperture 76. A cone 74 of X-rays emerges from aperture 76and impinges on anti-scatter grid 68 and imaging tube 70. The image thuscreated in imaging tube 70 is captured by camera 72. Depending on thespatial density distribution in an object such as patient 24 that istraversed by cone 74, each element of the CCD array of camera 72receives more or less light from imaging tube 70, and the correspondingpixel of the protective image produced by fluoroscope 22 iscorrespondingly darker or lighter.

Each element of the CCD array receives X-rays in a very narrow subconeof cone 74, corresponding to how much of cone 74 is subtended by theportion of the image created in imaging tube 70 that is focused ontothat element. The attenuation of this X-ray subcone is proportional tothe integrated density of the material traversed by the subcone betweenX-ray tube 63 and imaging tube 66. Conceptually, this subcone can betreated as a geometric ray from X-ray tube 63 to imaging tube 66.Because the disposition of fluoroscope 22 is measured by computer 50with the help of transmitter 30 and receiver 40, computer 50 knows thetrue location of X-ray tube 63 and every CCD element of camera 72 forevery image acquired by fluoroscope 22. Therefore, for every pixel of animage acquired by fluoroscope 22, computer 50 can form a mathematicalrepresentation of the corresponding ray.

According to the first aspect of the present invention, as applied tothe deployment of a stent in a coronary artery, a contrast agent isinjected into coronary artery tree 28, and then several images ofcoronary artery tree 28 are acquired, using fluoroscope 22, from severalangles. Projections of points of interest, such as the blockage to beopened by the stent, and such as branch points of coronary artery tree28 that must be traversed on the way to the blockage, appear on theseimages. These projections are picked on these images as displayed ondisplay unit 48. FIG. 3 shows, for three projections of one particularpoint-of-interest, three corresponding rays 78. In general, rays 78 donot intersect; but there is a point in space, labeled in FIG. 3 byreference numeral 80, such that the sum of the distances from point 80to rays 78 is less than the sum of the distances from any other point torays 78. Point 80 is referred to herein as the “point of nearest mutualapproach” of rays 78. Given mathematical representations of rays 78,computer 50 computes the coordinates of point 80 in the reference frameof transmitter 30. These coordinates are an estimate of the true spatiallocation of the point-of-interest corresponding to rays 78.

A minimum of two rays 78 are required to define point 80. Therefore, atleast two images of patient 24 must be acquired in order to estimate thelocations of all the points-of-interest.

The projections of the points-of-interest may be picked manually. Thepreferred method of manual picking is to acquire a set of images at anevenly spaced series of dispositions of fluoroscope 22 and to displaythe images successively and repeatedly on display 48 as a movie. All theimages are displayed in true mutual relative spatial locationorientation, on the basis of the measured dispositions of fluoroscope 22when the images were acquired. Along with the images is displayed anicon representing a point in space. Using an interactive input devicesuch as a mouse or a trackball, the user changes the coordinates of thepoint represented by the icon until the icon coincides with theprojection of the point-of-interest on each of the images. Note thatwhen this has been accomplished, the coordinates of the point areapproximately the true spatial coordinates of the point-of-interest, sothat the coordinates of the point serve as an alternative to the pointof nearest approach as an estimate of the true spatial location of thepoint-of-interest.

Alternatively, the projections of the points-of-interest are pickedmanually on the first acquired image and are tracked automatically tosubsequent images. Standard image processing and feature recognitiontechniques are used to track the projections of each point-of-interestfrom image to image.

The true spatial locations of the points-of-interest having beenestablished, the methods of WO 00/16684 are used to navigate the stentinto position. Note that at this point in the procedure, it is no longernecessary to display any of the acquired images; nor is it necessary toacquire further images, with the attendant exposure of both the medicalteam and the patient to additional X-radiation, and with the attendantadditional exposure of the patient to the contrast agent. Instead, onlyicons representing the locations of the points-of-interest are displayedon display unit 48, from any convenient point of view, along with anicon representative of the true location of catheter 26 relative to thepoints-of-interest, as determined using transmitter 30 and receiver 32to measure the disposition of catheter 26.

Note further that the point of view from which the icons are displayedneed not be, and generally is not, any of the points of view from whichthe images were acquired. In the present case of the points-of-interestbeing the branch points of coronary artery tree 28 and the targetlocation in coronary artery tree 28, the set of points-of-interestcontains all the information needed to navigate catheter 26 to thetarget location, and the images are redundant. In this context, thetarget location in coronary tree 28 is referred to herein as the “targetpoint-of-interest” and the branches of coronary artery tree 28 arereferred to herein as “intermediate point-of-interest”. Nevertheless, ifso desired, the points of interest may be displayed superposed on one ofthe images, from the point of view at which that image was acquired.

As an alternative to the projection picking and ray constructiondiscussed above, the projective images acquired using fluoroscope 22 aretransformed into an image volume, and the points-of-interest are pickedin the image volume. How this transformation is accomplished, despitethe relative mechanical instability of fluoroscope 22, is the subject ofthe second aspect of the present invention.

The mathematics of the tomographic transformation of a set of projectiveimages into an image volume is well-established, being described, forexample, in A. G. Ramm and A. I. Katsevich, The Radon Transform andLocal Tomography, CRC Press, 1996; in F. Natterer, The Mathematics ofComputerized Tomography, Wiley, 1989; in G. T. Herman et al., BasicMethods of Tomography and Inverse Problems, Hildger, 1987; and in G. T.Herman and Attila Kuba, Discrete Tomography, Birkhauser, 1999. All fourof these publications are incorporated by reference for all purposes asif fully set forth herein. In particular, Ramm and Katsevich, on pages276-302, discuss backprojection reconstruction in the case of a conicalX-ray beam geometry such as X-ray cone 74.

Standard tomographic reconstruction algorithms assume that the inputprojective images are acquired at regularly spaced angles around thetarget being imaged, or equivalently, in the terminology used herein, atregularly spaced dispositions of the projective imaging device. Theoperator of fluoroscope 22 moves fluoroscope 22 (manually or under thecontrol of computer 50) to successive nominal dispositions offluoroscope 22, as indicated by the controls of fluoroscope 22. At eachnominal disposition, the operator acquires a corresponding projectiveimage. Because of inaccuracies in the construction of a typicalfluoroscope 22, and because of the inherent mechanical flexibility ofcomponents of fluoroscope 22 such as C-arm 60, the actual disposition offluoroscope 22 when each projective image is acquired usually is notquite identical to the corresponding nominal disposition of fluoroscope22. The difference between the actual disposition of fluoroscope 22 andthe corresponding nominal disposition of fluoroscope 22 is sufficient tointroduce artifacts in the tomographically reconstructed image volume.

One way to overcome the mechanical instability of fluoroscope 22 is toignore the indications of the nominal disposition of fluoroscope 22 asindicated by the controls of fluoroscope 22, but instead to usetransmitter 30 and receiver 40 to measure the actual disposition offluoroscope 22. Computer 50 computes this actual disposition fromsignals received from receiver 40 in response to electromagneticradiation transmitted by transmitter 30. Computer 50 then displays thisactual disposition on display unit 48. The operator then uses thecontrols of fluoroscope 22 to move fluoroscope 22 until the actualdisposition displayed on display unit 48 is substantially identical tothe desired nominal disposition. Alternatively, computer 50 itself movesfluoroscope 22 to the desired nominal disposition, as illustratedschematically in FIG. 4, which shows further aspects of the mechanicalconstruction of fluoroscope 22 in (he context of other components of thesystem of the present invention as illustrated in FIG. 1B. As shown inFIG. 4, C-arm 60 is mounted in a yoke 82. A motor 88 in yoke 82 rotatesC-arm 60 about an axis 92 that is perpendicular to the plane of Figure'I. Yoke 82 itself is rigidly secured to a shaft 86 that is turned by amotor 90, so that motor 90 rotates yoke 82 about an axis 94 that is inthe plane of FIG. 4. Motor 90 is secured to a base 84. Just astransmitter 30 and receiver 40 are connected to computer 50 by wires 51,so motors 88 and 90 are connected to computer 50 by wires 51′. Ascomputer 50 receives signals from receiver 40 that are indicative of theactual disposition of fluoroscope 22, computer 50 computes the actualdisposition of fluoroscope 22 and operates motors 88 and 90 to moveC-arm 60 until the actual disposition of fluoroscope 22, as measuredusing transmitter 30 and receiver 40, is substantially the same as thedesired nominal disposition. The cooperative action of computer 50,transmitter 30, receiver 40 and motors 88 and 90 constitutes a feedbackloop for automatically moving fluoroscope 22 to the desired nominaldisposition.

A second way to overcome the mechanical instability of fluoroscope 22 isto move fluoroscope 22 to the nominal dispositions for acquiring theprojective images, as indicated by the controls of fluoroscope 22; tomeasure the actual dispositions of fluoroscope 22 after fluoroscope 22has been moved to these nominal dispositions; and to transform theacquired projective images into an image volume, not according to thenominal dispositions, but according to the actual dispositions. Thistransformation is done by a modified backprojection algorithm, asillustrated in FIG. 5. As noted above, for any disposition offluoroscope 22, computer 50 can form, for each pixel of the projectiveimage acquired at that disposition, a mathematical representations ofthe rays from X-ray tube 63 to the corresponding CCD element of camera72. The space occupied by the imaged portion of the body of patient 24is partitioned mathematically into a set of voxels. Some of these voxelsare illustrated in FIG. 5 as squares 96, it being understood that thisillustration is schematic, as voxels 96 actually are geometricallythree-dimensional, and in fact typically are cubes. Also shown in FIG. 5are some rays 98, corresponding to one disposition of fluoroscope 22,and some other rays 100, corresponding to another disposition offluoroscope 22. In general, each voxel 96 is traversed by many suchrays. The value assigned to each voxel 96 in the image volume is the sumof the pixels that correspond to the rays that traverse the voxel,weighted by the lengths of the portions of the rays that are inside thevoxel. For example, if the value of the pixel associated with ray 98 ais v_(a), if the value of the pixel associated with ray 100 c is v_(c),and if the value associated with ray 100 d is v_(d), then the valueassigned to voxel 96 e is l_(a)v_(a)+l_(c)v_(c)+l_(d)v_(d)+correspondingterms for all the other rays that traverse voxel 96 e.

A third way to overcome the mechanical instability of fluoroscope 22 isto estimate the actual dispositions of fluoroscope 22 from the acquiredprojective images and to then transform the projective images into animage volume according to the estimated actual dispositions instead ofaccording to the nominal dispositions. FIG. 6 shows a flow chart 110 ofhow this is accomplished. The input to flow chart 110 is a set 112 ofacquired projective images and the corresponding nominal dispositions.The output of flow chart 110 is an image volume 114 that is initializedin flow chart 110 according to the nominal dispositions and then iscorrected iteratively. In each iteration, acquired projective images 112are backprojected into a working version of image volume 114 on thebasis of the current estimate of the actual dispositions, corrections tothese dispositions are computed from the working version of image volume114 and from acquired projective images 112, and the corrections areapplied to the current dispositions to obtain a new estimate of thedispositions to be used in the next iteration.

In more detail, in box 116, the computational dispositions to be used inthe backprojection are initialized to the nominal dispositions. In box118, acquired projective images 112 are backprojected according to thecomputational dispositions to obtain image volume 114. At this stage,image volume 114 is an approximate rendition of the image volume thatwould have been obtained if acquired projective images had been acquiredat the computational dispositions. Therefore, in box 120, image volume114 is projected forward according to these dispositions to obtain a set122 of synthetic projective images, which are approximations of whatacquired projective images 112 would have been if acquired projectiveimages 112 had been acquired at the computational dispositions. In box124, synthetic projective images 122 are compared to acquired protectiveimages 112 to obtain estimates of the differences between thecomputational dispositions and the actual dispositions. For example, ifa particular synthetic projective image is rotated relative to thecorresponding acquired projective image, the degree of rotation is anindication of how much the corresponding computational disposition isrotated relative to the corresponding actual disposition. In box 126,these differences are compared to a threshold. If the differences aresufficiently small, the current version of image volume 114 is acceptedas the final image volume (box 128). Otherwise, the differences aresubtracted from the computational dispositions in box 130 and steps 118,120, 124 and 126 are repeated.

According to the third aspect of the present invention, as applied tothe deployment of a stent in a coronary artery, a contrast agent isinjected into the target coronary artery tree 28, and then severalimages of coronary artery tree 28 are acquired, using fluoroscope 22,from several angles. The best of these images to use as a road map, forsubsequent navigation of catheter 26 that bears the stent to the targetlocation in coronary artery tree 28, is selected. This image is referredto herein as the “guide image”. As each image is acquired, thecorresponding disposition of fluoroscope 22 is measured usingtransmitter 30 and receiver 40, and the corresponding disposition ofpatient 24 is measured using transmitter 30 and receiver 38. There aretwo ways to navigate catheter 26 with reference to the guide image.

The first way to navigate catheter 26 is to restore fluoroscope 22 tothe disposition of fluoroscope 22 at which the guide image was acquired.New images of coronary artery tree 28 are acquired using fluoroscope 22while catheter 26 is inserted into coronary artery tree 28. Theprojection of catheter 26 appears on the newly acquired images as ashadow. The guide image is superposed on each newly acquired image, sothat the instantaneous location of catheter 26 in coronary artery tree28 can be seen. Catheter 26 is directed accordingly towards the targetlocation in coronary artery tree 28.

The second way to navigate catheter 26 is to measure the disposition ofcatheter 26, using transmitter 30 and receiver 32,” to display the guideimage on display unit 48, and to display an icon, on display unit 48,that represents the shadow of catheter 26 that would ha-e been projectedonto the guide image if the guide image had been acquired with catheter26 at the measured disposition of catheter 26. Navigation of catheter 26with reference to the guide image then is conducted similarly tonavigation of catheter 26 with reference to both the guide image and thenewly acquired images according to the first way of navigating catheter26.

The first way of navigating catheter 26 minimizes the exposure ofpatient 24 to the contrast agent. The second way of navigating catheter26 also minimizes the exposure of patient 24 and the operators offluoroscope 22 to X-radiation.

The discussion, to this point, of the third aspect of the presentinvention, has assumed that patient 24 does not move between theacquisition of the guide image and the navigation of catheter 26. Ifpatient 24 move, then the new disposition of the body of patient 24,relative to the reference frame defined by transmitter 30, must bemeasured, using transmitter 30 and receiver 38, and the navigation ofcatheter 26 must take into account the change in the disposition of thebody of patient 24.

Under the first way of navigating catheter 26, fluoroscope 22 is moveduntil the relative dispositions of fluoroscope 22 and the body ofpatient 24 are the same as these dispositions were when the guide imagewas acquired. Let D_(f) ¹ represent the disposition of fluoroscope 22,relative to the reference frame defined by transmitter 30, when theguide image was acquired. Let D_(b) ¹ represent the disposition of thebody of patient 24, relative to the reference frame defined bytransmitter 30, when the guide image was acquired. Let D_(b) ² representthe present disposition of the body of patient 24, relative to thereference frame defined by transmitter 30. D_(b) ¹ and D_(b) ² arerelated by a translation T and a rigid rotation R:

D _(b) ² =RTD _(b) ¹

Fluoroscope 22 must be moved to a corresponding new disposition D_(f) ²,relative to the reference frame defined by transmitter 30:

D _(f) ² =RTD _(f) ¹

Note that dispositions D_(f) ¹ and D_(f) ² are measured usingtransmitter 30 and receiver 40, and that dispositions D_(b) ¹ and D_(b)² are measured using transmitter 30 and receiver 38.

Under the second way of navigating catheter 26, the icon that representscatheter 26, on the display on display unit 48, must be positioned inthat display as though the guide image had been acquired withfluoroscope 22 at disposition D_(f) ² instead of at disposition D_(f) ¹.

As discussed above in the context of the first aspect of the presentinvention, once all the points-of-incrust have been acquired, a displayof these points-of-interest on display unit 48 may be substituted forthe guide image. This has the advantage of allowing navigation ofcatheter 26 with reference to a display oriented according to whateverpoint of view is most convenient. Of course, if so desired, the displaymay be from the point of view from-which the guide image was acquired,and the points-of-interest may be superposed on the guide image.

During the acquisition of the points-of-interest, the disposition of thebody of patient 21 is measured using transmitter 30 and receiver 38. Ifpatient 24 moves between the acquisition of the points-of-interest andthe navigation of catheter 26, the disposition of the body of patient 24is measured again, and the mathematical transformations described aboveare used to adjust the display of the icons to ensure that the iconrepresenting catheter 26 still is displayed correctly relative to theicons representing the points-of-interest.

While the invention has been described with respect to a limited numberof embodiments, it will be appreciated that many variations,modifications and other applications of the invention may be made.

1-10. (canceled)
 11. A method of treating a body of a patient,comprising the steps of: simultaneously: acquiring a first image of atleast a portion of the body, using an imaging device, measuring adisposition of said imaging device relative to a reference frame, andmeasuring a disposition of the body relative to said reference frame:restoring said imaging device and the body to respective dispositionsthat are equivalent to said measured dispositions; and performing amedical procedure on the body with reference to said first image aftersaid restoring of said imaging device and of the body to said equivalentdispositions.
 12. The method of claim 11, wherein said measuring of saiddisposition of said imaging device is effected using a disposing systemthat includes a disposition implement associated with said imagingdevice and a disposing implement associated with said reference frame.13. The method of claim 11, wherein said measuring of said dispositionof said imaging device is effected using a disposing system thatincludes a disposing implement associated with said imaging device and adisposition implement associated with said reference frame.
 14. Themethod of claim 11, wherein said measuring of said disposition of thebody is effected using a disposing system that includes a dispositionimplement associated with the body and a disposing implement associatedwith said reference frame.
 15. The method of claim 11, wherein saidmeasuring of said disposition of the body is effected using a disposingsystem that includes a disposing implement associated with the body anda disposition implement associated with said reference frame.
 16. Themethod of claim 11, further comprising the step of: acquiring a secondimage of said at least portion of the body, using said imaging device,after said imaging device and the body have been restored to saidequivalent dispositions thereof; said medical procedure being performedwith reference to both said images.
 17. The method of claim 11, whereinsaid performing of said medical procedure includes navigating a probe toa point-of-interest in said at least portion of the body with referenceto said first image.
 18. The method of claim 17, further comprising thesteps of: acquiring a second image of said at least portion of the body,using said imaging device, after said imaging device and the body havebeen restored to said equivalent dispositions; said navigating beingwith reference to both said images.
 19. The method of claim 17, whereinsaid navigating includes measuring a disposition of said probe relativeto said reference frame.
 20. The method of claim 17, wherein saidmeasuring of said disposition of said probe is effected using adisposing system that includes a disposition implement associated withsaid probe and a disposing implement associated with said referenceframe.
 21. The method of claim 17, wherein said measuring of saiddisposition of said probe is effected using a disposing system thatincludes a disposing implement associated with said probe and adisposition implement associated with said reference frame.
 22. Themethod of claim 19, wherein said measuring of said disposition of saidimaging device, said measuring of said disposition of the body and saidmeasuring of said disposition of said probe are effected using a commondisposing system that includes a first disposition implement associatedwith said imaging device, a second disposition implement associated withthe body, a third disposition implement associated with said probe and acommon disposing implement associated with said reference frame.
 23. Themethod of claim 19, wherein said measuring of said disposition of saidimaging device, said measuring of said disposition of the body and saidmeasuring of said disposition of said probe are effected using a commondisposing system that includes a first disposing implement associatedwith said imaging device, a second disposing implement associated withthe body, a third disposing implement associated with said probe and acommon disposition implement associated with said reference frame.
 24. Amethod of treating a body of a patient, comprising the steps of:simultaneously: acquiring a first image of at least a portion of thebody, using an imaging device, measuring a disposition of said imagingdevice relative to a reference frame, and measuring a first dispositionof the body relative to said reference frame; measuring a seconddisposition of the body relative to said reference frame; and performinga medical procedure on the body with reference to said first image andwith reference to all three said dispositions.
 25. The method of claim24, wherein said measuring of said disposition of said imaging device iseffected using a disposing system that includes a disposition implementassociated with said imaging device and a disposing implement associatedwith said reference frame.
 26. The method of claim 24, wherein saidmeasuring of said disposition of said imaging device is effected using adisposing system that includes a disposing implement associated withsaid imaging device and a disposition implement associated with saidreference frame.
 27. The method of claim 24, wherein said measuring ofsaid dispositions of the body is effected using a disposing system thatincludes a disposition implement associated with the body and adisposing implement associated with said reference frame.
 28. The methodof claim 24, wherein said measuring of said dispositions of the body iseffected using a disposing system that includes a disposing implementassociated with the body and a disposition implement associated withsaid reference frame.
 29. The method of claim 24, wherein saidperforming of said medical procedure includes navigating a probe to apoint-of-interest in said at least portion of the body.
 30. The methodof claim 29, wherein said navigating includes measuring a disposition ofthe probe relative to said reference frame.
 31. The method of claim 30,wherein said measuring of said disposition of said probe is effectedusing a disposing system that includes a disposition implementassociated with said probe and a disposing implement associated withsaid reference frame.
 32. The method of claim 30, wherein said measuringof said disposition of said probe is effected using a disposing systemthat includes a disposing implement associated with said probe and adisposition implement associated with said reference frame.
 33. Themethod of claim 30, wherein said measuring of said disposition of saidimaging device, said measuring of said dispositions of the body and saidmeasuring of said disposition of said probe are effected using a commondisposing system that includes a first disposition implement associatedwith said imaging device, a second disposition implement associated withthe body, a third disposition implement associated with said probe and acommon disposing implement associated with said reference frame.
 34. Themethod of claim 30, wherein said measuring of said disposition of saidimaging device, said measuring of said dispositions of the body and saidmeasuring of said disposition of said probe are effected using a commondisposing system that includes a first disposing implement associatedwith said imaging device, a second disposing implement associated withthe body, a third disposing implement associated with said probe and acommon disposition implement associated with said reference frame.